The present invention relates to equipment and a method for forwarding a frame in a computer network, and more specifically, to improvement of a technology of controlling congestion of a traffic.
The Ethernet (registered trademark) that realizes a computer network transmits and receives data divided in a unit, called a frame, and permits frame discarding on a communication path, such as of repeater equipment. For an application that does not permit data loss by the frame discarding, a PAUSE frame for a flow control is specified in IEEE 802.3x as an extended standard. The flow control is performed to the link that connects a transmitting side and a receiving side. If it is assumed that the receiving side of the link cannot receive a frame correctly for a reason of the congestion etc., the receiving side of the link will transmit the PAUSE frame to the transmitting side. The transmitting side of the link that received the PAUSE frame temporarily suspends frame transmission. By processings on these transmitting side and receiving side of the link, the flow control of the link is performed, which prevents the frame discarding caused by an incapability of the receiving side to receive the frame.
On the other hand, with densification of servers and acceleration of Ethernet used for Local Area Networks (LANs) as a background, there has been accelerated movement of integrated LAN/SAN where a Storage Area Network (SAN) for storage access that has been built separately from the LAN so far is built using the Ethernet and is integrated to the LAN, so that network interfaces, cables, and network devices are curtailed to achieve operations more efficiently. Moreover, thanks to development of server virtualization, an environment where multiple virtual machines are made to operate on a single physical sever and a single LAN is shared with multiple networks has become used in general. In these environments, it is necessary to flow multiple traffics whose characteristics and requirements are different on a physically single strand of Ethernet cable. As a technique of distinguishing these traffics logically, a Virtual LAN (VLAN) specified in IEEE 802.1Q has spread widely. In the VLAN, a VLAN tag is attached to each frame and the traffic is distinguished by a priority and a VLAN ID that are included in the VLAN tag. The use of the VLAN enables to logically divide a single strand of a physical link and to use each of them.
In the traffic of storage access in an integrated LAN/SAN environment, the frame discarding is not permitted. However, since the flow control by the PAUSE is performed per physical link, if the congestion occurs in any one of the links logically divided by the VLAN and the PAUSE frame is transmitted to effect temporal suspension of the transmission, the frame transmission of the traffics that flow in other logical links that share the same physical link will also be suspended. That is, there occurs a problem that the congestion in a part of the traffic hinders communications of other traffics because the multiple traffics share a single link.
As a conventional technology to solve this, there is known a technique of specifying the PAUSE frame that is independent for every logical link (for example, Japanese Unexamined Patent Application Publication No. 2007-174152 and IEEE 802.1Qbb/D2.3, “Draft Standard for Local and Metropolitan Area Networks—Virtual Bridged Local Area Networks—Amendment: Priority-based Flow Control,” Issue date Sep. 9, 2010).
Japanese Unexamined Patent Application Publication No. 2007-174152 describes “A congestion control system having a network switch that includes a congestion detection part that detects the congestion of a transmission frame inputted from multiple input/output ports and a PAUSE frame sending part that sends out the PAUSE frame to the input/output port at which the congestion detection part detected the congestion, characterized by being provided with an extended PAUSE frame sending part that uses an extended transmission frame being the transmission frame added with virtual LAN information instead of the transmission frame and an extended PAUSE frame being the PAUSE frame added with virtual LAN information instead of the PAUSE frame, and sends the extended PAUSE frame to the input/output port acting for the PAUSE frame sending part. Furthermore, Japanese Unexamined Patent Application Publication No. 2007-174152 describes that “It is characterized in that especially, the virtual LAN information is made to be the VLAN-ID value of the VLAN tag of the IEEE 802.3x standard. Alternatively, it is characterized in that the virtual LAN information is made to be a priority value of the VLAN tag of the IEEE 802.3x standard.”
Moreover, IEEE 802.10bb/D2.3, “Draft Standard for Local and Metropolitan Area Networks—Virtual Bridged Local Area Networks—Amendment: Priority-based Flow Control,” Issue date Sep. 9, 2010 prescribes an extended PAUSE frame that includes a PAUSE instruction of the VLAN tag for every priority and the flow control for every logical link using the PAUSE frame as IEEE 802.1 Qbb.